The present invention relates in general to the field of microelectronic packages, components thereof and methods to bond such components and obtain such packages. In particular, the present invention relates to techniques to obtain metal interconnects based on metal pads (e.g., copper pads) structured to ease the penetration of the reducing agent.
Various bonding processes are known, which involve solders, such as the so-called mass-reflow solder, copper-pillar solder reflow and copper-pillar compression techniques. Such techniques allow a range of interconnect pitches to be obtained (namely from 20 to 130 μm), with different qualities of interconnects.
The above techniques all involve an isothermal sintering step to bind opposite components of the package. It has also been proposed to apply copper-paste on copper pillars of one of these components, in order to bind the components by sintering. Formic acid enriched nitrogen is typically used as a reducing agent to remove the copper oxide formed during the material fabrication and handling during the bonding process. Other reducing agents, such as formic gas can be used as well. This makes it possible to obtain a satisfactory electrical conduction through the interconnects.